1. Field of Invention
This invention relates to image segmentation and compression. In particular, the invention is directed to using segmentation information to enable compression and decompression of image data by both lossless and lossy techniques.
2. Description of Related Art
JPEG (Joint Photographic Experts Group) is recognized as a good technique for compressing contones and filtered high frequency halftones. This lossy compression technique is especially effective in compressing color images. Compressing images in a luminance/chrominance space and using the fact that the human visual system does not need the same resolution for color information as it does for intensity results in high compression ratios.
However, lossy techniques are not well suited for compressing and decompressing text images. The linear transforms used in lossy techniques have difficulty compressing sharp edges. Consequently, these edges tend to blur and soften through multiple compression and decompression operations.
Lossless compression techniques, such as Lempel Ziv (LZ), are better suited for compressing text and low frequency halftone images. These lossless compression techniques provide high compression ratios and compression processing speeds, and are also advantageous for image data that contains significant amounts of repeated data. However, lossless compression techniques are not as efficient when compressing a high frequency halftone, contone or background image where high resolution is not required.